Golf ball material, golf ball and method for preparing golf ball material

ABSTRACT

The invention provides a golf ball material composed of an ionomeric resin composition obtained by melt-blending under applied heat one or more compounds selected from among UV/EB-curable materials with, in the presence of a peroxide, a non-ionomeric thermoplastic resin and an ionomeric resin; or of an ionomeric resin composition obtained by using, instead of the ionomeric resin, an acid-containing polymer base of the ionomeric resin and subjecting the acid-containing polymer composition similarly prepared by melt-blending under applied heat to an acid-neutralizing reaction with a metal ionic species. Methods for preparing such a material, and golf balls which include as a component therein a molding made of the golf ball material are also provided. The golf ball material has a good thermal stability, flow and processability, and can thus be used to obtain high-performance golf balls endowed with an excellent abrasion resistance, scuff resistance, durability and flexibility without a loss of rebound.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. patent application Ser. No. 12/199,193,filed Aug. 27, 2008 now U.S. Pat. No. 8,106,125. The entire disclosureof the prior application is considered part of the disclosure of theaccompanying divisional application, and is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball material which has a goodthermal stability, flow and processability, and from whichhigh-performance golf balls endowed with excellent properties such asrebound, durability, flexibility and scuff resistance can be obtained.The invention also relates to a method for preparing such a golf ballmaterial, and to a golf ball which includes as a component therein amolding made from such a golf ball material.

In recent years, ionomeric resins have been widely used in golf ballmaterials. Ionomeric resins are ionic copolymers of an olefin such asethylene with an unsaturated carboxylic acid such as acrylic acid,methacrylic acid or maleic acid, in which some of the acidic groups areneutralized with metal ions such as sodium, lithium, zinc or magnesium.These resins have excellent characteristics in terms of the durability,rebound and scuff resistance of the ball.

At present, the base resins used in golf ball cover materials aregenerally ionomeric resins, but a variety of modifications are beingmade to address the constant desire by players for golf balls having asuitable degree of flexibility, a high rebound and an excellent flightperformance.

For example, to improve the rebound and flow of ionomer materials,Patent Document 1 (U.S. Pat. No. 5,312,857), Patent Document 2 (U.S.Pat. No. 5,306,760), Patent Document 3 (U.S. Pat. No. 6,100,321), PatentDocument 4 (U.S. Pat. No. 6,653,382) and Patent Document 5 (U.S. Pat.No. 6,777,472) describe materials composed of an ionomeric resin towhich a large amount of a metallic soap (a metal salt of a higher fattyacid) has been added.

However, the metallic soap in these ionomer materials undergodecomposition and vaporization during injection molding, generating alarge amount of fatty acid gases. As a result, molding defects tend toarise. Moreover, the gases that have formed deposit on the surface ofthe molding, markedly lowering its paintability. Moreover, when suchionomer materials are used as golf ball cover materials, because a largeamount of low-molecular-weight metallic soap (a metal salt of a higherfatty acid) is included, the durability of the golf ball significantlydeteriorates, making the ionomer material entirely unfit for practicaluse.

In addition, materials in the form of simple molten mixtures of aflexible thermoplastic resin and an ionomer have been developed (PatentDocument 6:JP-A 2003-180878). However, even though such a materialappears to be uniform during the production process, there has been someconcern that when the material is injection molded to form a particulargolf ball layer, the high shear forces in the mold will causedelamination to occur in the layer formed by the molten mixture.

An ionomer material for golf balls which has recently been developed isa homogeneous-phase, high-rebound resilience material that has aninterpenetrating polymer network (IPN) structure (Patent Document 7:U.S. Patent Application No. 2004/0044136; Patent Document 8:U.S. PatentApplication No. 2004/0242802; Patent Document 9: U.S. Pat. No.7,026,399; Patent Document 10: U.S. Pat. No. 7,175,545). The ionomermaterial is obtained by blending a first ingredient such as anethylene-(meth)acrylic acid copolymer with a second ingredient that is adifferent type of thermoplastic resin to form a resin composition, thenadding a metal ionic species as a third ingredient so as to neutralizethe acid on the first ingredient dispersed in the resin composition.However, in such a production method, if the different type ofthermoplastic resin used as the second ingredient is poorly compatibleor completely incompatible with the ionomeric resin matrix therebycreated, when injection molding is carried out using these materials toform a particular golf ball layer, the high shear forces in the moldsometimes cause delamination to occur within the layer, raising concernsover a decline in the properties of the golf ball. In particular, therehas been a tendency for a strong decline in the scuff resistance.

-   -   Patent Document 1: U.S. Pat. No. 5,312,857    -   Patent Document 2: U.S. Pat. No. 5,306,760    -   Patent Document 3: U.S. Pat. No. 6,100,321    -   Patent Document 4: U.S. Pat. No. 6,653,382    -   Patent Document 5: U.S. Pat. No. 6,777,472    -   Patent Document 6: JP-A 2003-180878    -   Patent Document 7: U.S. Patent Application No. 2004/0044136    -   Patent Document 8: U.S. Patent Application No. 2004/0242802    -   Patent Document 9: U.S. Pat. No. 7,026,399    -   Patent Document 10: U.S. Pat. No. 7,175,545

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball material which has a good thermal stability, flow andprocessability, and moreover which, when injection-molded and used as agolf ball component, is able to suppress delamination within a golf balllayer and thus enables high-performance golf balls endowed withexcellent properties such as flexibility, durability and scuffresistance to be obtained without a loss of rebound. Another object ofthe invention is to provide a method for preparing such a golf ballmaterial. A further object of the invention is to provide a golf ballwhich includes as a component therein a molding made from such a golfball material.

As a result of extensive investigations, the inventors have discoveredthat an ionomeric resin composition obtained by compounding a materialcurable by exposure to, for example, sunlight, x-rays, ultraviolet light(UV), electron beams (EB) or a plasma arc (i.e., a UV/EB-curablematerial) with, in the presence of a peroxide and without carrying outexposure to sunlight, x-rays, ultraviolet light, electron beams or aplasma arc, the thermoplastic resin used in the present invention, thenmelt-blending the resulting mixture under applied heat with an ionomericresin is capable of suppressing delamination when injection molded as agolf ball material. The inventors have also found that an ionomericresin composition obtained by compounding the above UV/EB-curablematerial with, in the presence of a peroxide, a thermoplastic resin andan acid-containing polymer that is the base of an ionomeric resin so asto form an acid-containing polymer composition, then adding thereto ametal ionic species and carrying out an acid-neutralizing reaction, canserve as a golf ball material which suppresses delamination wheninjection molded.

In addition, the inventors have found that when an ionomeric resincomposition prepared by including as one component therein aUV/EB-curable material in the absence of a peroxide is subjected toprolonged aging for a period of about 5 days or more, the effects of theUV/EB-curable material emerge as a result of the automatic oxidativecrosslinking of the UV/EB-curable material.

The inventors have additionally learned that such ionomeric resincompositions have a surprisingly good thermal stability, flow andprocessability and, when used as a golf ball component, are idealmaterials for forming high-performance golf balls endowed with excellentproperties such as flexibility, durability and scuff resistance withouta loss of rebound.

From additional investigations, the inventors have also found that golfballs which include a molding of such a golf ball material as acomponent therein (here and below, “component” refers to the covermaterial in a two-piece solid golf ball composed of a core and a coverwhich encases the core, or to the cover material or intermediate layermaterial in a multi-piece solid golf ball composed of a core of at leastone layer, at least one intermediate layer which encases the core, and acover of at least one layer which encases the intermediate layer), havean excellent flexibility, durability and scuff resistance without a lossof rebound.

Accordingly, the present invention provides the following golf ballmaterial, methods for preparing such a golf ball material, and golf ballwhich includes as a component therein a molding of such a golf ballmaterial.

[I] Golf Ball Material

A golf ball material containing an ionomeric resin composition whichincludes the following components (i) to (iii):

-   (i) one or more compounds selected from among UV/EB-curable    materials;-   (ii) a non-ionomeric thermoplastic resin; and-   (iii) an ionomeric resin.    [II] Methods for Preparing Golf Ball Materials-   [1] A method for preparing a golf ball material, which method    includes the steps of: initially melt-blending (i) at least one    compound selected from among UV/EB-curable materials with (ii) a    non-ionomeric thermoplastic resin; then adding (iii) an ionomeric    resin or an ionomeric resin together with the acid-containing    polymer base thereof and melt-blending so as to obtain an ionomeric    resin composition.-   [2] A method for preparing a golf ball material, which method    includes the steps of: melt-blending (i) at least one compound    selected from among UV/EB-curable materials with (ii) a    non-ionomeric thermoplastic resin and (iii) the acid-containing    polymer base of an ionomeric resin; then adding an oxygen-containing    inorganic metal compound-type metal ionic species and carrying out    an acid-neutralizing reaction while melt-blending so as to obtain an    ionomeric resin composition.-   [3] A method for preparing a golf ball material, which method    includes the steps of: adding together (i) at least one compound    selected from among UV/EB-curable materials, (ii) a non-ionomeric    thermoplastic resin and (iv) a peroxide, and melt-blending at a    temperature at which the peroxide does not decompose prematurely;    then adding (iii) an ionomeric resin or an ionomeric resin and the    acid-containing polymer base thereof and melt-blending at or above    the temperature at which the peroxide decomposes so as to obtain an    ionomeric resin composition having an interpenetrating polymer    network (IPN) structure.-   [4] A method for preparing a golf ball material, which method    includes the steps of: adding together (i) at least one compound    selected from among UV/EB-curable materials, (ii) a non-ionomeric    thermoplastic resin, (iii) the acid-containing polymer base of an    ionomeric resin, and (iv) a peroxide, and melt-blending at a    temperature at which the peroxide does not decompose prematurely;    then adding an oxygen-containing inorganic metal compound-type metal    ionic species and melt-blending at or above the temperature at which    the peroxide decomposes so as to both induce a grafting reaction    on (i) the at least one compound selected from among UV/EB-curable    materials and neutralize the acid within (iii) the acid-containing    polymer of an ionomeric resin, and thereby obtain an ionomeric resin    composition having an interpenetrating polymer network structure.    [III] Golf Balls

Golf balls which include as a component therein a molding made of any ofthe above golf ball materials. In particular, golf balls wherein any ofthe above golf ball materials is used as a cover material in a two-piecesolid golf ball composed of a core and a cover which encases the core,or as a cover material or intermediate layer material in a multi-piecesolid golf ball composed of a core of at least one layer, one or moreintermediate layers which encases the core, and a cover of at least onelayer which encases the intermediate layer.

The present invention uses any one of the following ionomer resincompositions (A) to (C).

Ionomeric Resin Composition (A)

An ionomeric resin composition (A) obtained by melt-blending underapplied heat one or more compounds selected from among UV/EB-curablematerials with, in the presence of a peroxide and without carrying outexposure to sunlight, x-rays, ultraviolet light, electron beams or aplasma arc, a non-ionomeric thermoplastic resin and an ionomeric resin,or the ionomeric resin and an acid-containing polymer of the basethereof.

Ionomeric Resin Composition (B)

An ionomeric resin composition (B) obtained by carrying out meltblending under applied heat using, instead of the above ionomer, anacid-containing polymer base of the ionomer at a temperature up to thedecomposition temperature of the peroxide so as to prepare anacid-containing polymer composition, then carrying out anacid-neutralizing reaction using an oxygen-containing inorganiccompound-type metal ionic species.

Ionomeric Resin Composition (C)

An ionomeric resin composition (C) obtained by aging rather thanincluding a peroxide in above ionomeric resin composition (A) or (B).

The above ionomeric resin compositions (A) to (C) suppress delaminationand have a good thermal stability, flow and processability duringinjection molding. Golf balls using such compositions exhibit a goodperformance, such as excellent flexibility, durability and scuffresistance, with no loss of rebound. The present invention providesmethods for preparing such golf ball materials, and golf balls whichinclude as a component therein moldings of such golf ball materials.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The golf ball material of the present invention includes an ionomericresin composition composed of (i) one or more compounds selected fromamong UV/EB-curable materials, (ii) a non-ionomeric thermoplastic resin,(iii) an ionomeric resin, an ionomeric resin and/or an acid-containingpolymer base of an ionomeric resin, or, instead of the ionomeric resin,an acid-containing polymer base of an ionomeric resin and anoxygen-containing inorganic metal compound, and (iv) a peroxide.Alternatively, the golf ball material includes an ionomeric resincomposition composed of above ingredients (i), (ii) and (iii). Themethod for preparing such a golf ball material involves melt-blending(i) the above one or more compounds selected from among UV/EB-curablematerials with (ii) the above non-ionomeric thermoplastic resin and (iv)the above peroxide at a temperature at which the peroxide does notdecompose, then adding (iii) the above ionomeric resin so as to obtain agolf ball material which includes (A) an ionomeric resin composition ofthe invention as an essential ingredient. Alternatively, the method forpreparing such a golf ball material involves adding together (i) theabove one or more compounds selected from UV/EB-curable materials, (ii)the above non-ionomeric thermoplastic resin, (iii) the acid-containingpolymer base of the above ionomeric resin instead of the ionomeric resinitself, and (iv) a peroxide; melt-blending the ingredients at or below atemperature at which the peroxide decomposes; then adding anoxygen-containing inorganic metal compound-type metal ionic species andmelt-blending under applied heat at or above the temperature at whichthe peroxide decomposes so as to obtain a golf ball material whichincludes (B) an ionomeric resin composition of the invention as anessential ingredient.

Moreover, when a resin composition obtained by a procedure that does notinvolve adding a peroxide during the formulation of (A) or (B) issubjected to aging treatment, a golf ball material containing (C) anionomeric resin composition of the invention is obtained.

The present invention relates to ionomeric resin systems, whichgenerally have a poor compatibility with non-ionomeric thermoplasticresins. Specifically, it provides an ionomeric resin composition thatincludes a non-ionomeric thermoplastic resin, which ionomeric resincomposition suppresses delamination during injection molding.

Moreover, this invention, the object of which is to prepare a golf ballmaterial that, in an ionomeric resin composition containing therein anon-ionomeric thermoplastic resin, suppresses delamination duringinjection molding, has a good thermal stability, flow and processabilityand, when used in a particular layer of a golf ball, can be used toproduce golf balls endowed with excellent flexibility, durability andscuff resistance without a loss of rebound, was arrived at based on thediscovery that UV/EB-curable materials function as an excellentinterphase crosslinking agent between ionomeric resins and thermoplasticresins.

UV/EB-curable materials are commonly used for topcoating thesurface-most layer of a golf ball under exposure to, for example,x-rays, ultraviolet light (UV), electron beams (EB) or a plasma arc.However, the present invention is not an application of this type.Instead, it is intended to make it possible to carry out interphasecrosslinking between a non-ionomeric thermoplastic resin and anionomeric resin by, in the melt-blending of a non-ionomericthermoplastic resin with an ionomeric resin in the presence of aperoxide, the concomitant use of a UV/EB-curable material having askeletal structure similar to that of the non-ionomeric thermoplasticresin. That is, the inventors conceived of the idea of forming aninterpenetrating polymer network structure, and have found that theresulting ionomeric resin composition (A) is useful as a golf ballmaterial in which delamination during injection molding can besuppressed.

The inventors have also found that an ionomeric resin composition (B)with an interpenetrating polymer network (IPN) structure, obtained bycompounding the above-described UV/EB-curable material, in the presenceof a peroxide, with a non-ionomeric thermoplastic resin and theacid-containing polymer base of an ionomeric resin (i.e., one or moreacid-containing polymers selected from the group consisting ofolefin-unsaturated carboxylic acid copolymers, olefin-unsaturatedcarboxylic acid-unsaturated carboxylic acid ester terpolymers,unsaturated carboxylic anhydride-containing polymers, unsaturateddicarboxylic acid-containing polymers and unsaturated dicarboxylic acidhalf ester-containing polymers) to form an acid-containing polymercomposition, then melt-blending into the acid-containing polymercomposition an oxygen-containing inorganic metal compound-type metalionic species so as to induce both a grafting reaction on theUV/EB-curable material and also an acid-neutralizing reaction by themetal ionic species, is useful as a golf ball material in whichdelamination during injection molding is suppressed.

The inventors have additionally found that an ionomeric resincomposition (C) obtained by subjecting a resin blend formulated in thesame way as above ionomeric resin composition (A) or (B), but without aperoxide, to aging treatment is useful as a golf ball material in whichdelamination during injection molding is suppressed.

Because the UV/EB-curable material having a skeletal structure similarto the skeletal structure of the non-ionomeric thermoplastic resin usedin the invention further improves the compatibility with non-ionomericthermoplastic resins, the inventors have found that, as a result, a golfball material containing an ionomeric resin composition having a moreuniform IPN structure can be obtained.

In the present invention, by including a UV/EB-curable material in theionomeric resin composition, non-ionomeric thermoplastic resin layers,which are incompatible or poorly compatible with ionomeric resin layers,can also be incorporated with good uniformity, thereby ultimately givinga golf ball material in which delamination is suppressed duringinjection molding, which has a good thermal stability, flow andprocessability, and which, when used in golf balls, exhibits excellentproperties, such as durability, scuff resistance and flexibility,without a loss of rebound.

In the invention, if the UV/EB-curable material is not used in thenon-ionomeric thermoplastic resin-containing ionomeric resin compositionpreparing step, delamination will usually tend to arise when injectionmolding is carried out. On the other hand, using an excess amount of theUV/EB-curable material will lead to gel formation, making the ionomericresin composition non-uniform, and ultimately preventing the physicalproperties that are the object of the inventive golf ball material frombeing achieved.

In the practice of the invention, a UV/EB-curable material, a peroxide,a non-ionomeric thermoplastic resin and an ionomeric resin aremelt-blended in the non-ionomeric thermoplastic resin-containingionomeric resin composition (A) preparing step. It is preferable tofirst melt-blend the UV/EB-curable material, the peroxide and thenon-ionomeric thermoplastic resin in a temperature range at which theperoxide does not decompose, then add the ionomeric resin and melt-mixthe components at or above the temperature at which the peroxidedecomposes.

Alternatively, in the present invention, in the non-ionomericthermoplastic resin-containing ionomeric resin composition (B) preparingstep, by first melt-blending a UV/EB-curable material, a peroxide, anon-ionomeric thermoplastic resin and an acid-containing polymer base ofan ionomeric resin in a temperature range at which the peroxide does notdecompose, then adding an oxygen-containing inorganic metalcompound-type metal ionic species and melt-blending at or above theperoxide decomposition temperature, an ionomeric resin compositionhaving an IPN structure can be obtained as a result of both a graftingreaction on the UV/EB-curable material and an acid-neutralizing reactionby the metal ionic species.

In this case, the UV/EB-curable material, peroxide and non-ionomericthermoplastic resin are first melt-blended in a temperature range atwhich the peroxide does not decompose, the acid-containing polymer issubsequently melt-blended in a temperature range at about which theperoxide does not decompose, then the oxygen-containing inorganic metalcompound-type metal ionic species is added and melt-blended at or abovethe peroxide decomposition temperature.

Also, in the present invention, in the step of preparing theabove-described ionomeric resin compositions (A) and (B), by not using aperoxide and subjecting the resin blend to aging treatment, it ispossible to obtain an ionomeric resin composition (C) having resinproperties similar to those of ionomeric resin compositions (A) and (B).

The aging treatment conditions include a temperature of from about 5° C.to about 80° C., preferably from about 10° C. to about 70° C., and morepreferably from about 20° C. to about 60° C. The aging period is atleast about 5 days, preferably at least about 7 days, and morepreferably at least about 10 days, with the upper limit being about 100days. The relative humidity during aging is from about 10% to about 80%,preferably from about 20% to about 70%, and even more preferably fromabout 30% to about 55%.

It is desirable for the UV/EB-curable material used in the presentinvention to be one having a skeletal structure similar to the skeletalstructure of the non-ionomeric thermoplastic resin that is used. Thecompatibility between the UV/EB-curable material and the non-ionomericthermoplastic resin can thus be further enhanced, enabling an ionomericresin composition having a more uniform IPN structure to be obtained.

Examples of the one or more types of compound selected from amongUV/EB-curable materials that may be used in the invention include, butare not limited to, materials in which a portion of the main-chainskeleton is selected from among polyester, polyether, urethane,acrylate, butadiene, epoxy, carbonate and rosin structures and whichhave at least two functional groups with an ethylenically unsaturatedbond per molecule, the functional groups with an ethylenicallyunsaturated bond being polymerizable function groups of one or moretypes selected from among acrylic (CH₂═CHCO—), methacrylic(CH₂═C(CH₃)CO—), allyl (CH₂═CHCH—) and vinyl (CH₂═CH—) groups.

Specific examples include polyester acrylates [EBECRYL 657 (fourfunctional groups; about 125,000 mPa·sec/25° C.; number-averagemolecular weight Mn, about 1,500), EBECRYL 853 (three functional groups;about 80 mPa·sec/25° C.; Mn, about 470) and EBECRYL 1830 (six functionalgroups; about 50,000 mPa·sec/25° C.; Mn, about 1,500), all produced byDaicel-Cytec Co., Ltd.; and Aronix M6250 (two functional groups; about500 Pa·sec/25° C.; number-average molecular weight Mn, about 1,000)produced by Toagosei Co., Ltd.]; polyether acrylates [BLEMMER-ADE600(two functional groups; about 70 mPa·sec/25° C.; Mn, about 750) producedby NOF Corporation, and UV-6640B (two functional groups; about 20,000mPa·sec/50° C.; Mn, about 5,000) produced by Nippon Synthetic ChemicalIndustry Co., Ltd.]; urethane acrylates [SHIKOH UV-7510B (threefunctional groups; about 2,000 mPa·sec/50° C.; Mn, about 3,500) andSHIKOH UV-7000B (three functional groups about 25,000 mPa·sec/50° C.;Mn, about 3,500), both produced by Nippon Synthetic Chemical IndustryCo., Ltd.; and Ebecryl 270 (two functional groups; about 3,000mPa·sec/50° C.; Mn, about 1,500) produced by CYTEC]; epoxy (bisphenol A)acrylates [V #700 (two functional groups; about 1,000 Pa·sec/25° C.; Mn,about 500) and V #540 (two functional groups; about 15,000 mPa·sec/50°C.; Mn, about 540), both produced by Osaka Organic Chemical Industry,Ltd.]; carbonate acrylates [UV-3210EA (two functional groups; about3,000 mPa·sec/25° C.; Mn, about 9,000) and UV-3310B (two functionalgroups; about 55,000 mPa·sec/50° C.; Mn, about 5,000), both produced byNippon Synthetic Chemical Industry Co., Ltd.]; butadiene acrylates[BAC-45 (two functional groups; about 4,500 mPa·sec/25° C.; Mn, about3,000) produced by Osaka Organic Chemical Industry, Ltd.]; rosinacrylates [BEAMSET 102 (three functional groups; about 35,000mPa·sec/40° C.; Mn, about 5,000) produced by Arakawa ChemicalIndustries, Ltd.; and BANBEAM UV-22A (three functional groups; about530,000 mPa·sec/25° C.; Mn, about 5,000) and BANBEAM UV-22C (threefunctional groups; about 120,000 mPa·sec/25° C.; Mn, about 5,000), bothproduced by Harima Chemicals, Inc.]; polyether allyls [Polyglycol AA600(two functional groups; about 27,000 mPa·sec/20° C.; Mn, about 600) andPolyglycol AAl200 (two functional groups; about 41,000 mPa·sec/20° C.;Mn, about 1,200), both produced by Clariant]; and polyether vinyls[TEGVE (two functional groups; about 3.4 mPa·sec/25° C.; Mn, 202)produced by Nippon Carbide Industries Co., Inc.].

The amount of the above UV/EB-curable material included per 100 parts byweight of the combined amount of the non-ionomeric thermoplastic resinand the ionomeric resin or the acid-containing polymer that is the baseresin thereof, is from 0.05 to 30 parts by weight, preferably from 0.1to 20 parts by weight, and more preferably from 0.5 to 10.0 parts byweight. If too much UV/EB-curable material is included, the resultingionomeric resin composition may exhibit a dramatic decline in melt flowrate (MFR) and undergo gel formation, making it impossible to obtain anormal molded piece. Conversely, if too little is added, the resultingionomeric resin composition may give rise to delamination duringinjection molding, possibly leading to a poor scuff resistance and a lowrebound, and thus having an adverse influence on the properties of thegolf ball obtained as the finished product.

The peroxide used together with the above UV/EB-curable material may besuitably selected with reference to the decomposition temperaturethereof and the melting temperature at which the non-ionomericthermoplastic resin employed is capable of being kneaded. Specifically,use is typically made of one or more peroxides selected from amongdicumyl peroxide (one-minute half-life temperature, 175° C.), di-t-butylperoxide (185° C.), 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne (194°C.), n-butyl-4,4-di(t-butylperoxy)valerate (173° C.),di(2-t-butylperoxyisopropyl) benzene (175° C.), di-t-hexyl peroxide(177° C.) and p-menthanehydroperoxide (200° C.). It is desirable to setthe amount of the peroxide included, per 100 parts by weight of thecombined amount of the non-ionomeric thermoplastic resin and theionomeric resin and/or the acid-containing polymer base thereof, atpreferably from 0.05 to 20 parts by weight, more preferably from 0.08 to15 parts by weight, even more preferably from 0.1 to 10 parts by weight,and most preferably from 0.5 to 5.0 parts by weight.

The non-ionomeric thermoplastic resin used in the invention may be oneor more selected from among polyolefin elastomers (including polyolefinsand metallocene-catalyzed polyolefins), polystyrene elastomers,polyacrylate polymers, polyamide elastomers, polyurethane elastomers,polyester elastomers and polyacetals. Illustrative examples includepolyethylene methacrylate, maleic anhydride-grafted polyethylene ethylacrylate, hexamethylene diisocyanate (HDI)-poly-ε-caprolactone (PCL),4,4′-dicyclohexylmethane diisocyanate (H12-MDI)-polytetramethyleneglycol (PTMG), polystyrene-butylene, polybutylene terephthalate,polyether polyamide and polyoxymethylene. The weight ratio(non-ionomeric thermoplastic resin/ionomeric resin or theacid-containing polymer base thereof) is preferably from 1/99 to 99/1,more preferably from 5/95 to 95/5, and even more preferably from 10/90to 90/10.

The ionomer resin used in the invention may be one or more ionomerresins obtained by neutralizing, within a degree of neutralization rangeof from 5 to 90 mol %, one or more polymers having an acid content offrom 0.5 to 30 wt %, preferably from 1.0 to 25 wt %, and selected fromamong olefin-unsaturated carboxylic acid copolymers, olefin-unsaturatedcarboxylic acid-unsaturated carboxylic acid ester terpolymers,unsaturated carboxylic anhydride-containing polymers, unsaturateddicarboxylic acid-containing polymers, and unsaturated dicarboxylic acidhalf ester-containing polymers with one or more metal cations selectedfrom among groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA,VIB, VIIB AND VIIIB of the periodic table.

Specific examples include 60 mol % Zn (degree of neutralization withzinc)-polyethylene-methacrylic acid copolymers, 40 mol % Mg (degree ofneutralization with magnesium)-polyethylene-methacrylic acid copolymers,and 40 mol % Mg (degree of neutralization withmagnesium)-polyethylene-methacrylic acid-isobutylene acrylateterpolymers.

In the present invention, in cases where the non-ionomeric thermoplasticresin has basic functional groups such as amino groups or imino groups,to avoid the reaction of a dicarboxylic acid or an acid anhydridethereof with the basic functional groups, preferred use may be made of,as the acid-containing polymer base of the above-described ionomericresin, a polymer containing an acid (e.g., carboxylic acid) other than adicarboxylic acid or acid anhydride thereof. Such a polymer isexemplified by an olefin-unsaturated carboxylic acid copolymer having anacid content of from 0.5 to 30 wt %, and preferably from 1.0 to 25 wt %.The number of carbons on the olefin is generally at least 2 and not morethan 8, preferably not more than 6. Illustrative examples of sucholefins include ethylene, propylene, butene, pentene, hexene, hepteneand octene. The use of ethylene is especially preferred. Illustrativeexamples of the unsaturated carboxylic acid include acrylic acid,methacrylic acid, dimethylacrylic acid and ethacrylic acid. The use ofacrylic acid or methacrylic acid is especially preferred.

Alternatively, an olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester terpolymer may be used as the polymer containingan acid other than a dicarboxylic acid or acid anhydride thereof. Theunsaturated carboxylic acid ester is preferably a lower alkyl ester ofan unsaturated carboxylic acid. For example, use may be made of one ormore selected from among methyl methacrylate, ethyl methacrylate, propylmethacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate,propyl acrylate and butyl acrylate. The use of butyl acrylate (n-butylacrylate, isobutyl acrylate) is especially preferred. The content,expressed as a weight ratio (non-ionomeric thermoplasticresin/acid-containing polymer), is typically from 1/99 to 99/1,preferably from 5/95 to 95/5, and more preferably from 10/90 to 90/10.

In the invention, the acid-containing polymer composition prepared fromthe one or more compounds selected from among UV/EB-curable materials,the peroxide, the non-ionomeric thermoplastic resin and theacid-containing polymer base of an ionomeric resin is subjected to anacid-neutralizing reaction with a metal ionic species, enabling anionomeric resin composition having an IPN structure to be obtained. Theoxygen-containing inorganic metal compound-type metal ionic species usedat this time is one or more selected from the group consisting oflithium carbonate, sodium carbonate, potassium carbonate, magnesiumcarbonate, zinc carbonate, magnesium hydroxide, magnesium oxide, calciumhydroxide, calcium oxide and zinc oxide. It is preferable for theseoxygen-containing inorganic metal compounds to be used in the form ofnanoparticles or a masterbatch. The amount in which these metal ionicspecies are included (degree of neutralization) will vary with the acidcontent of the acid-containing polymer base of an ionomeric resin thatis used, with the degree of neutralization being preferably from 1 to 95mol %, more preferably from 5 to 90 mol %, and even more preferably from10 to 80 mol %. If the degree of neutralization is too high, the flowproperties of the ionomeric resin composition may deteriorate (i.e., themelt index may decrease), which may make injection molding difficult tocarry out. Moreover, during injection molding, the heat generated byshear may increase, causing thermal degradation and delamination of thenon-ionomeric thermoplastic resin included within the ionomeric resincomposition. Conversely, if the degree of neutralization is too low,although the composition will have flow properties, due to a decline inthe degree of ionic crosslinking, the mechanical strength of theionomeric resin composition itself may decrease, possibly leading to adecline in ball strength and a low durability when the composition isused as a golf ball material.

It is desirable for the acid-neutralizing reaction on theacid-containing polymer composition by the oxygen-containing inorganicmetal compound-type metal ionic species to be carried out using a ventedtwin-screw extruder having arranged thereon a screw segment with akneading disc zone.

Where appropriate for the intended use, optional additives may beincluded in the golf ball material of the invention. When the golf ballmaterial of the invention is to be used as a cover material, in additionto the essential ingredients described above, additives such aspigments, dispersants, antioxidants, ultraviolet absorbers and lightstabilizers may also be included. Such additives are included in anamount, per 100 parts by weight of the essential ingredients, ofpreferably at least 0.1 part by weight, and more preferably at least 0.5part by weight, but preferably not more than 10 parts by weight, andmore preferably not more than 4 parts by weight.

The golf ball material of the invention has a specific gravity ofpreferably at least 0.9, more preferably at least 0.92, and even morepreferably at least 0.94, but preferably not more than 1.3, morepreferably not more than 1.2, and even more preferably not more than1.05.

Moldings obtained using the inventive golf ball material have a Shore Dhardness of preferably at least 40, and more preferably at least 45, butpreferably not more than 75, and more preferably not more than 70. Ifthe Shore D hardness is too high, there may be a marked decline in thefeel of the resulting golf ball on impact. On the other hand, if theShore D hardness is too low, the rebound of the ball may decrease.

The inventive golf ball material which is an ionomeric resin compositionmay be used as the cover material in a two-piece solid golf ballcomposed of a core and a cover encasing the core, or as the covermaterial or intermediate layer material in a multi-piece solid golf ballcomposed of a core of at least one layer, one or more intermediatelayers which encases the core, and a cover of at least one layer whichencases the intermediate layer.

In the inventive golf ball material and method of preparation thereof,the principal component is either (1) an ionomeric resin compositionobtained by melt-blending under applied heat one or more compoundsselected from among UV/EB-curable materials with, in the presence orabsence of a peroxide, a non-ionomeric thermoplastic resin and anionomeric resin, or (2) an ionomeric resin composition having an IPNstructure obtained by likewise melt-blending under applied heat one ormore compounds selected from among UV/EB-curable materials with, in thepresence or absence of a peroxide, a non-ionomeric thermoplastic resin,but using, instead of the ionomeric resin, an acid-containing polymerbase of the ionomeric resin, then carrying out a reaction in which theacid is neutralized with a metal ionic species. As a result, when thegolf ball material is injection-molded, delamination is suppressed andthe golf ball material exhibits a good thermal stability, flow andprocessability, enabling high-performance golf balls endowed withexcellent properties such as flexibility, durability and scuffresistance to be obtained.

EXAMPLES

Examples are given below by way of illustration and not by way oflimitation. The twin-screw extruder used in the examples of theinvention to carry out the reactions (“reaction twin-screw extruder”)had a screw diameter of 32 mm, an overall L/D ratio of 41, and an L/Dratio for the kneading disc zone which was 40% of the overall L/D ratio.Moreover, the extruder had a vacuum vent port and was equipped with adevice for injecting water under pressure. Material preparation wassuitably carried out by using a 5-liter pressure kneader and pelletizingthe resulting kneaded mass with a 40 mm diameter twin screw/single-screwextruder.

Example 1

An acid-containing polymer composition was obtained by first kneadingthe respective ingredients, including the UV/EB-curable material UV/EB-4having a urethane skeleton (injected with a liquid feeder), butexcluding the magnesium hydroxide masterbatch MgMB, within thetwin-screw extruder in the proportions indicated in Table 1 and at amelting temperature at which the peroxide PO-3 does not decompose (170°C.). Next, the amount of MgMB shown in Table 1 was added to theacid-containing polymer composition, then both an acid-neutralizingreaction to 50 mol % neutralization of the acid-containing base resinincluded and decomposition of the PO-3 were carried out in the reactiontwin-screw extruder at a temperature setting of 210° C., thereby givinga uniform ionomeric resin composition. The melt flow rate (MFR) andhardness of the resulting ionomeric resin composition are shown in Table1.The ionomeric resin composition in this example had a suitable, lowhardness and a melt flow rate appropriate for injection molding. Next,using this ionomeric resin composition as the cover material fortwo-piece golf balls, the composition was injection molded over a coreof crosslinked butadiene rubber (core diameter, 38.9 mm; weight, 36.0 g;deflection, 3.35 mm) using an injection molding machine, therebyproducing two-piece golf balls (diameter, 42.7 mm; weight, 45.5 g). Thegolf balls were then evaluated. The results are shown in Table 1. Afterinjection molding, the golf balls were trimmed, yielding finished golfballs having a smooth surface free of burrs and endowed with goodabrasion resistance, scuff resistance, ball durability, initial velocityand coefficient of restitution (COR).

The magnesium hydroxide masterbatch was prepared according to the methoddescribed in Japanese Patent Application No. 2005-227691. That is, a5-liter pressure kneader (manufactured by Naniwa Machinery ManufacturingCo., Ltd.; temperature setting, 100° C.) was charged with a combinedamount of 2.0 kg of Nucrel N0200H (an ethylene-methacrylic acid-isobutylacrylate terpolymer produced by DuPont) as the base polymer for themasterbatch and magnesium hydroxide Mg(OH)₂ (average particle size, 0.8μm; produced by Kyowa Chemical Industry Co., Ltd.) in a weight ratio(N0200H/Mg(OH)₂) of 50/50, and mixing was carried out for 20 minutesunder an applied pressure of 0.49 MPa at a rotor speed of 35 rpm and ata mixing temperature controlled within a range of 120 to 130° C. Themixture was discharged as a strand from a 40 mm diametertwin-screw/single-screw extruder (Naniwa Machinery Manufacturing Co.,Ltd.; temperature setting, 180° C.), then pelletized. The melt flow rate(MFR) of the resulting Magnesium hydroxide-containing masterbatch havinga Mg(OH)₂ content of 50 wt % was 2.3 g/10 min (measured at 190° C. undera load of 2,160 g). This masterbatch is designated below as “MgMB.”

Example 2

An acid-containing polymer composition was obtained by kneading therespective ingredients, including the UV/EB-curable material UV/EB-4having a urethane skeleton (injected with a liquid feeder), butexcluding the peroxide PO-3, within the twin-screw extruder in theproportions indicated in Table 1 and at a melting temperature of 170° C.Next, the amount of the MgMB shown in Table 1 was added to theacid-containing polymer composition, then an acid-neutralizing reactionto 50 mol % neutralization of the acid-containing base resin includedwas carried out in the reaction twin-screw extruder at a temperaturesetting of 210° C., thereby giving a uniform ionomeric resincomposition. A hot press set to 180° C. was used to form the ionomericresin composition into 2 mm thick sheets having a length of 100 mm and awidth of 100 mm. In addition, the resulting ionomeric resin compositionwas subjected to the same procedure as in Example 1 and injection-moldedin an injection molding machine, thereby producing two-piece golf balls.The sheets and the golf balls thus produced were held at rest underaging conditions of 23±5° C. and 45 to 55% relative humidity for 25days, following which the various properties were evaluated. The resultsare shown in the table. The properties were substantially the same as inExample 1.

Example 3

A uniform ionomeric resin composition was obtained by first kneading therespective ingredients, including the UV/EB-curable material UV/EB-3having a butadiene skeleton, but excluding nanoZnO, within a 5-literpressure kneader in the proportions indicated in Table 1 and at atemperature (110° C.) at which the peroxide PO-2 does not decompose,then adding a predetermined amount of the nanoZnO shown in Table 1 tothe resulting acid-containing polymer composition in which butadiene hasbeen formulated and subsequently carrying out both an acid-neutralizingreaction to 35 mol % neutralization of the acid-containing base resinincluded and decomposition of the PO-2 at a temperature of 170° C. Themelt flow rate and hardness of the resulting ionomeric resin compositionare shown in Table 1.These results indicate that the ionomeric resincomposition had a suitable, low hardness and a melt flow rateappropriate for injection molding. This ionomeric resin composition wassubjected to the same golf ball injection molding procedure as inExample 1, thereby producing two-piece golf balls. The injection-moldedgolf balls were trimmed, yielding finished golf balls having a smoothsurface free of burrs and endowed with good abrasion resistance, scuffresistance, ball durability, initial velocity and coefficient ofrestitution (COR).

Example 4

An acid-containing polymer composition was obtained by kneading therespective ingredients, including the UV/EB-curable material UV/EB-2having a polyether skeleton (using a liquid feeder), but excludingnanoZnO, within the twin-screw extruder in the proportions indicated inTable 1 and at a melting temperature (170° C.) at which the peroxidePO-1 does not decompose. Next, the amount of the nanoZnO shown in Table1 was added to the acid-containing polymer composition, following whichboth an acid-neutralizing reaction to 60 mol % neutralization of theacid-containing base resin included and decomposition of the PO-1 werecarried out in the reaction twin-screw extruder at a temperature settingof 210° C., thereby giving a uniform ionomeric resin composition. Themelt flow rate and hardness of the ionomeric resin composition thusobtained are shown in Table 1.These results indicate that the ionomericresin composition had a suitable, high hardness and a melt flow rateappropriate for injection molding. This ionomeric resin composition wassubjected to the same golf ball injection molding procedure as inExample 1, thereby producing two-piece golf balls. The injection-moldedgolf balls were trimmed, yielding finished golf balls having a smoothsurface free of burrs and endowed with good abrasion resistance, scuffresistance, ball durability, initial velocity and coefficient ofrestitution (COR).

Example 5

An acid-containing polymer composition was obtained by mixing therespective ingredients, including the UV/EB-curable material UV/EB-1having a polyester skeleton (using a liquid feeder), but excludingnanoZnO, within the twin-screw extruder in the proportions indicated inTable 1 and at a melting temperature (180° C.) at which the peroxidePO-3 does not decompose. Next, the amount of the nanoZnO shown in Table1 was added to the acid-containing polymer composition, following whichboth an acid-neutralizing reaction to 45 mol % neutralization of theacid-containing base resin included and decomposition of the PO-1 werecarried out in the reaction twin-screw extruder at a temperature settingof 210° C., thereby giving a uniform ionomeric resin composition. Themelt flow rate and hardness of the ionomeric resin composition thusobtained are shown in the table. These results indicate that theionomeric resin composition had a suitable, moderate hardness and a meltflow rate appropriate for injection molding. This ionomeric resincomposition was subjected to the same golf ball injection moldingprocedure as in Example 1, thereby producing two-piece golf balls. Theinjection-molded golf balls were trimmed, yielding finished golf ballshaving a smooth surface free of burrs and endowed with good abrasionresistance, scuff resistance, ball durability, initial velocity andcoefficient of restitution (COR).

Comparative Example 1

As a comparative example for Example 1 of the invention, an ionomericresin composition was prepared by mixing the respective ingredients,except for the UV/EB-curable material UV/EB-4 having a urethaneskeleton, in the proportions shown in Table 1 and using the sameprocedure as in Example 1, following which two-piece golf balls wereproduced. After injection molding, the golf balls were trimmed, yieldingfinished golf balls having a smooth surface free of burrs and a goodabrasion resistance. However, compared with Example 1 of the inventionin which the UV/EB-curable material UV/EB-4 having a urethane skeletonwas included, the ball tended to have an inferior scuff resistance, balldurability, initial velocity and coefficient of restitution. Thisdemonstrated the importance of including a UV/EB-curable material.

Comparative Example 2

In this example, carried out as a comparative example for Example 3 ofthe invention, the reaction twin-screw extruder (temperature setting,210° C.) was used to neutralize a base resin (Base Resin-2) with nanoZnOin the ingredient amounts shown in Table 1, excluding the UV/EB-curablematerial UV/EB-3 having a butadiene skeleton, thereby forming a zincionomer having a degree of neutralization of 35 mol %. Next, using a5-liter pressure kneader set to the PO-2 decomposition temperature (170°C.), the zinc ionomer, butadiene rubber and the peroxide PO-2 weremelt-blended in the amounts shown in Table 1, thereby giving anionomeric resin composition. Using this ionomeric resin composition,golf balls were injection-molded in the same way as in Example 1,thereby giving two-piece golf balls. The injection-molded golf ballswere trimmed, yielding finished golf balls which had burrs thereon(coarse surface) and, compared with Example 3, had a markedly decreasedball durability and a lower initial velocity and coefficient ofrestitution. In contrast with Example 3 of the invention, a melt blendcomposed of an ionomer and butadiene rubber was prepared in thiscomparative example. As a result, an IPN structure was difficult to formby the procedure of Example 3 and a UV/EB-curable material was notincluded. Hence, the golf ball properties were inferior.

Comparative Example 3

In this example, carried out as a comparative example for Example 4 ofthe invention, an ionomeric resin composition was prepared by mixing therespective ingredients, except for the UV/EB-curable material UV/EB-2having a polyether skeleton and the peroxide PO-1, in the proportionsshown in Table 1 and using the same procedure as in Example 4, followingwhich two-piece golf balls were produced. After injection molding, thegolf balls were trimmed, yielding finished golf balls having a smoothsurface free of burrs and a good abrasion resistance. However, comparedwith Example 4 of the invention in which the UV/EB-curable materialUV/EB-2 having a polyether skeleton and the peroxide PO-1 were included,the ball tended to have an inferior scuff resistance, ball durability,initial velocity and coefficient of restitution. This demonstrated theimportance of including a UV/EB-curable material and a peroxide.

TABLE 1 Example Comparative Example Items 1 2* 3 4 5 1 2 3 i)UV/EB-curable agents UV/EB-1 — — — — 1.5 — — — UV/EB-2 — — — 0.5 — — — —UV/EB-3 — — 1.0 — — — — — UV/EB-4 1.5 1.5 — — — — — — ii) Peroxides PO-1— — — 0.20 — — — — PO-2 — — 1.0 — — — 1.0 — PO-3 0.25 — — — 0.15 0.25 —— iii) Non-ionomers TPEE — — — — 8.5 — — — POM — — — 4.5 — — — 5.0 BR —— 9.0 — — — 10.0 — TPU 18.5 18.5 — — — 20.0 — — iv) Ionomers & Baseresins Ionomer-1 — — — — 40 — — — Ionomer-2 — — — 50.0 — — — 50.0Ionomer-3 5.0 5.0 — — — 5.0 — — Base resin-1 — — — 45.0 40 — — 45.0 Baseresin-2 — — 90.0 — — — 90.0 — Base resin-3 10.0 10.0 — — — 10.0 — — Baseresin-4 15.0 15.0 — — — 15.0 — — Base resin-5 25.0 25.0 — — 10.0 25.0 —— Base resin-6 25.0 25.0 — — — 25.0 — — v) Cationic sources nanoZnO — —3.0 1.9 1.45 — 3.0 1.9 MgMB 3.65 3.65 — — — 3.65 — — vi) Filler &Pigment Titanium dioxide 1.5 1.5 — 2.0 2.0 1.5 — 2.0 Blue pigment 0.070.07 — 0.02 0.02 0.07 — 0.02 Specific gravity 0.994 0.994 0.953 0.9940.974 0.994 0.953 0.994 MFR (g/10 min at 190° C., 2160 g) 1.1 1.2 8.31.6 2.0 1.5 10.1 2.1 Hardness (Shore D) 52 52 54 65 61 52 54 64Deflection (mm) at 23° C. 3.06 3.07 2.89 2.72 2.26 3.06 2.87 2.74Initial velocity (m/sec) at 23° C. 77.53 77.51 77.57 77.51 77.43 75.3876.42 77.23 Average C.O.R 0.745 0.744 0.771 0.798 0.792 0.739 0.7680.791 Shot number (Durability) 204 211 116 122 290 106 22 90 Scuffresistance at 23° C. 2 2 2 2 2 3 4 3 Abrasion resistance (Sand) GoodGood Good Good Good Good Poor Good GB surface after trimming SmoothSmooth Smooth Smooth Smooth Smooth Rough Smooth *25-day aging time

The materials appearing in the above table are explained below.

a. UV/EB-1

Aronix M6250 (a polyester-based acrylate having two functional groups;about 500 mPa·sec/25° C.; number-average molecular weight, about 1,000),produced by Toagosei Co., Ltd.

b. UB/EB-2

TEGVE (a polyether-based vinyl having two functional groups; about 3.4mPa·sec/25° C.; number-average molecular weight, about 202), produced byNippon Carbide Industries Co., Inc.

c. UV/EB-3

BAC-45 (a butadiene-based acrylate having two functional groups; about4,500 mPa·sec/25° C.; number-average molecular weight, about 3,000),produced by Osaka. Organic Chemical Industry, Ltd.

d. UV/EB-4

SHIKOH UV-7510B (a urethane-based acrylate having three functionalgroups; about 2,000 mPa·sec/50° C.; number-average molecular weight,about 3,500), produced by Nippon Synthetic Chemical Industry Co., Ltd.

e. PO-1

Di-t-butyl peroxide (1-minute half-life temperature, 185° C.), producedby NOF Corporation.

f. PO-2

Dicumyl peroxide (1-minute half-life temperature, 175° C.), produced byNOF Corporation.

g. PO-3

2,5-Dimethyl-2,5-di(t-butylperoxy)-3-hexane (1-minute half-lifetemperature, 194° C.), produced by NOF Corporation.

h. TPEE

Hytrel 4047 (polyester polyether, Shore D 40), produced by DuPont.

i. POM

AMILUS 5731 (polyacetal; MFR, 9.0 g/10 min; m.p., 166° C.), produced byToray Industries, Inc.

j. BR

Maleic anhydride-modified BR01 (polybutadiene; cis-1,4-bond content,96%; nickel polymerization catalyst; produced by JSR Corporation), a BSPexperimental product.

k. TPU

5-Norbornene-2,3-dicarboxylic acid-modified aliphatic polyurethane(HMDI-PCL, produced by DIC-Bayer), a BSP experimental product.

l. Ionomer-1

S8527 (a sodium ionomer; Shore D 56), produced by DuPont.

m. Ionomer-2

S8940 (a sodium ionomer; Shore D 63), produced by DuPont.

n. Ionomer-3

S9945 (a zinc ionomer; Shore D 61), produced by DuPont.

o. Base Resin-1

Nucrel 960 (methacrylic acid, 15 wt %: MFR, 60 g/10 min), produced byDuPont.

p. Base Resin-2

Nucrel 2050H (methacrylic acid, 20 wt %: MFR, 500 g/10 min), produced byDuPont.

q. Base Resin-3

Nucrel 599 (methacrylic acid, 10 wt %: MFR, 500 g/10 min), produced byDuPont.

r. Base Resin-4

AC5120H (acrylic acid, 15.6 wt %: MFR, >500 g/10 min), produced by TomenPlastics Corporation.

s. Base Resin-5

AN 4319 (methacrylic acid, 8.0 wt %: MFR, 50 g/10 min), produced byDuPont.

t. Base Resin-6

Escor 5200 (acrylic acid, 15.0 wt %: MFR, 36 g/10 min), produced byExxonMobil Chemical.

u. nanoZnO

The zinc oxide NANOFINE-50 (average particle size, 20 nm; particle sizedistribution, 1 to 100 nm; proportion having a particle size of 0.05 μmor less, 60%), produced by

Sakai Chemical Industry Co., Ltd.

v. MgMB

Magnesium hydroxide/ethylene-methacrylic acid-isobutyl acrylateterpolymer=50/50 wt %.

w. Titanium Dioxide

Tipaque PF737, produced by Ishihara Sangyo Kaisha.

x. Blue Pigment

Pigment Blue 29, produced by Toyo Ink.

The test items in the table are explained below.

MFR (g/10 min)

The melt flow rate was measured in accordance with JIS-K 7210 at a testtemperature of 190° C. and a test load of 21.18 N (2.16 kgf).

Shore D Hardness

The Shore D hardness was measured in accordance with ASTM D-2240.

Deflection

The golf ball was placed on a steel plate and the deflection (mm) by theball when compressed under a final load of 1,275 N (130 kgf) from aninitial load of 98 N (10 kgf) was measured. The test was carried out ata temperature of 23±11° C.

Initial Velocity

The initial velocity was measured using an initial velocity measuringapparatus of the same type as the USGA drum rotation-type initialvelocity instrument approved by the R&A. The ball was kept isothermallyat a temperature of 23±1° C. for at least 3 hours, then tested at thesame temperature.

The ball was hit using a 250-pound (113.4 kg) head (striking mass) at animpact velocity of 143.8 ft/s (43.83 m/s). Ten balls were each hit twotimes. The time taken by the ball to traverse a distance of 6.28 ft(1.91 m) was measured and used to compute the initial velocity of theball. This cycle was carried out over a period of about 15 minutes.

Coefficient of Restitution (COR)

The ball was fired from an air cannon against a steel plate at avelocity of 43 m/s, and the rebound velocity was measured. Thecoefficient of restitution (COR) is the ratio of the rebound velocity tothe initial velocity of the ball.

Shot Number (Durability)

The durability of the golf ball was evaluated using an ADC Ball CORDurability Tester produced by Automated Design Corporation (U.S.). Aball was fired using air pressure and made to repeatedly strike twometal plates arranged in parallel. The average number of shots requiredfor the ball to crack was treated as its durability. Average values wereobtained by furnishing four balls of the same type for testing,repeatedly firing each ball until it cracked, and averaging the numberof shots required for the respective balls to crack. The type of testerused was a horizontal COR durability tester, and the incident velocityof the balls on the metal plates was 43 m/s.

Scuff Resistance

The golf balls were held at a temperature of 23±1° C. and hit at a headspeed of 33 m/s using a pitching wedge mounted on a swing robot machine,after which damage from the impact was visually rated according to thefollowing scale.

Best: 1 point Better: 2 points Good (ordinary): 3 points Poor: 4 pointsPoorer: 5 points Poorest: 6 pointsAbrasion Resistance

A tubular container having a five liter capacity was filled with 15 golfballs and 1.7 liters of sand, after which the contents were mixed at 50rpm for 2 hours. The balls were then removed and, based on a visualdetermination of the extent of surface marring and decreased gloss dueto abrasion, the abrasion resistance was rated as follows.

Best

Better

Good (ordinary)

Poor

Poorer

Poorest

Ball Appearance after Surface Abrasion

The injection-molded golf ball was surface abraded (trimmed) with a #500grinding wheel for 3.5 seconds, following which the surface appearanceof the ball was rated as follows.

Smooth

Less rough

Rough

1. A method for preparing a golf ball material, comprising the steps of:initially melt-blending (i) at least one compound selected from amongUV/EB-curable materials wherein a portion of a main-chain skeleton ofthe compound is selected from the group consisting of polyester,polyether, urethane, acrylate, butadiene, epoxy, carbonate and rosinstructures, and which have at least two functional groups with anethylenically unsaturated bond per molecule, the functional groups withan ethylenically unsaturated bond being polymerizable functional groupsof one or more types selected from the group consisting of acrylic(CH₂═CHCO—), methacrylic (CH₂═C(CH₃)CO—), allyl (CH₂═CHCH—) and vinyl(CH₂═CH—) groups with (ii) a non-ionomeric thermoplastic resin; thenadding (iii) an ionomeric resin or an ionomeric resin together with theacid-containing polymer base thereof and melt-blending so as to obtainan ionomeric resin composition.
 2. The method for preparing a golf ballmaterial of claim 1, further comprising the step of subjecting theionomeric resin composition to aging treatment.
 3. The method forpreparing a golf ball material of claim 2, wherein aging treatment iscarried out under the following conditions: a temperature of from about5° C. to about 80° C., and a period of standing of from about 5 days toabout 100 days.
 4. The method for preparing a golf ball material ofclaim 1, wherein the UV/EB-curable materials are selected from the groupconsisting of polyester acrylates, polyether acrylates, urethaneacrylates, epoxy (bisphenol A) acrylates, carbonate acrylates, butadieneacrylates, rosin acrylates, polyether allyls and polyether vinyls.
 5. Amethod for preparing a golf ball material, comprising the steps of:initially melt-blending (i) at least one compound selected from amongUV/EB-curable materials wherein a portion of a main-chain skeleton ofthe compound is selected from the group consisting of polyester,polyether, urethane, acrylate, butadiene, epoxy, carbonate and rosinstructures, and which have at least two functional groups with anethylenically unsaturated bond per molecule, the functional groups withan ethylenically unsaturated bond being polymerizable functional groupsof one or more types selected from the group consisting of acrylic(CH₂═CHCO—), methacrylic (CH₂═C(CH₃)CO—), allyl (CH₂═CHCH—) and vinyl(CH₂═CH—) groups with (ii) a non-ionomeric thermoplastic resin; thenadding (iii) the acid-containing polymer base of an ionomeric resin;then adding an oxygen-containing inorganic metal compound-type metalionic species and carrying out an acid-neutralizing reaction whilemelt-blending so as to obtain an ionomeric resin composition.
 6. Themethod for preparing a golf ball material of claim 2, wherein theUV/EB-curable materials are selected from the group consisting ofpolyester acrylates, polyether acrylates, urethane acrylates, epoxy(bisphenol A) acrylates, carbonate acrylates, butadiene acrylates, rosinacrylates, polyether allyls and polyether vinyls.
 7. A method forpreparing a golf ball material, comprising the steps of: adding together(i) at least one compound selected from among UV/EB-curable materialswherein a portion of a main-chain skeleton of the compound is selectedfrom the group consisting of polyester, polyether, urethane, acrylate,butadiene, epoxy, carbonate and rosin structures, and which have atleast two functional groups with an ethylenically unsaturated bond permolecule, the functional groups with an ethylenically unsaturated bondbeing polymerizable functional groups of one or more types selected fromthe group consisting of acrylic (CH₂═CHCO—), methacrylic(CH₂═C(CH₃)CO—), allyl (CH₂═CHCH—) and vinyl (CH₂═CH—) groups, (ii) anon-ionomeric thermoplastic resin and (iv) a peroxide, and melt-blendingat a temperature at which the peroxide does not decompose prematurely;then adding (iii) an ionomeric resin or an ionomeric resin and theacid-containing polymer base thereof and melt-blending at or above thetemperature at which the peroxide decomposes so as to obtain anionomeric resin composition having an interpenetrating polymer network(IPN) structure.
 8. The method for preparing a golf ball material ofclaim 7, wherein the UV/EB-curable materials are selected from the groupconsisting of polyester acrylates, polyether acrylates, urethaneacrylates, epoxy (bisphenol A) acrylates, carbonate acrylates, butadieneacrylates, rosin acrylates, polyether allyls and polyether vinyls.
 9. Amethod for preparing a golf ball material, comprising the steps of:adding together (i) at least one compound selected from amongUV/EB-curable materials wherein a portion of a main-chain skeleton ofthe compound is selected from the group consisting of polyester,polyether, urethane, acrylate, butadiene, epoxy, carbonate and rosinstructures, and which have at least two functional groups with anethylenically unsaturated bond per molecule, the functional groups withan ethylenically unsaturated bond being polymerizable functional groupsof one or more types selected from the group consisting of acrylic(CH₂═CHCO—), methacrylic (CH₂═C(CH₃)CO—), allyl (CH₂═CHCH—) and vinyl(CH₂═CH—) groups, (ii) a non-ionomeric thermoplastic resin, (iii) theacid-containing polymer base of an ionomeric resin, and (iv) a peroxide,and melt-blending at a temperature at which the peroxide does notdecompose prematurely; then adding an oxygen-containing inorganic metalcompound-type metal ionic species and melt-blending at or above thetemperature at which the peroxide decomposes so as to both induce agrafting reaction on (i) the at least one compound selected from amongUV/EB-curable materials and neutralize the acid within (iii) theacid-containing polymer base of an ionomeric resin, and thereby obtainan ionomeric resin composition having an interpenetrating polymernetwork structure.
 10. The method for preparing a golf ball material ofclaim 9, wherein the oxygen-containing inorganic metal compound-typemetal ionic species is one or more selected from the group consisting oflithium carbonate, sodium carbonate, potassium carbonate, magnesiumcarbonate, zinc carbonate, magnesium hydroxide, magnesium oxide, calciumhydroxide, calcium oxide and zinc oxide, and the oxygen-containinginorganic metal compound is used in the form of nanoparticles or amasterbatch.
 11. The method for preparing a golf ball material of claim9, wherein the acid-neutralizing reaction on the acid-containing polymercomposition by the oxygen-containing inorganic metal compound-type metalionic species is carried out using a vented twin-screw extruder havingarranged thereon a screw segment with a kneading disc zone.
 12. Themethod for preparing a golf ball material of claim 9, wherein theUV/EB-curable materials are selected from the group consisting ofpolyester acrylates, polyether acrylates, urethane acrylates, epoxy(bisphenol A) acrylates, carbonate acrylates, butadiene acrylates, rosinacrylates, polyether allyls and polyether vinyls.